The present invention relates to a method for directly bonding a metal member to a ceramic member, and to a laminated body of ceramic and metal members obtained by this method.
A conventional method for bonding a metal member to a ceramic member of alumina or the like is known in which a molybdenum paste is baked on the surface of the ceramic member, and nickel plating is then performed to securely bond the metal member thereto. This method is adopted when the ceramic involved is an oxide. However, when the ceramic is made of a substance other than an oxide, such as a nitride, another method is adopted. According to this method, a recessed area is formed in one of the members to be bonded, while a projection is formed on the other member in a corresponding pattern, and the two members are then shrink fitted to each other. The former method is complex in procedure and requires two heat treatment steps. On the other hand, the latter method can provide only a weak adhesive strength since the two members are bonded only by a clamping force.
To solve this problem, still another method has been proposed in which a metal member is directly bonded to a ceramic member. This method includes a first method in which a metal member is bought into direct contact with a ceramic member and the two members are heated in a gas atmosphere containing a bonding agent; and, a second method in which a metal member is surface-treated with a bonding agent, the treated metal member is brought into contact with a ceramic member and the two members are heated in an inert gas atmosphere (e.g., U.S. Pat. No. 3,994,430).
However, these methods have a common disadvantage in that, when the ceramic member consists of a ceramic which does not contain a bonding agent at all or contains such agent only in a small amount, bonding of such a ceramic member to a metal member is very difficult.
This means that if a ceramic member consists of a nonoxide-type ceramic, such as silicon nitride, and the bonding agent is oxygen, bonding of the ceramic member to a metal member will be difficult. The reasons for this are considered to be attributable to the facts that a eutectic of a metal and a bonding agent which is produced at the interface between the ceramic member and the metal member has poor wettability with a ceramic member consisting of a nonoxide-type ceramic, and that oxygen contained in a ceramic member contributes in some manner to producing a stable compound with a metal.